Question: My air conditioner was not working and it turned out to be a problem with a part on my furnace. How is my furnace and AC connected?
Answer: The standard split air conditioning system consists of an outdoor condenser and an indoor evaporator coil that fits onto some kind of air handler, usually a gas or electric furnace. This coil is installed between the air handler and the supply ducting.
The indoor and outdoor components are connected to each other by the refrigerant piping (called a lineset) and control wiring. The ductwork attached to the air handler is an important part of both of these systems.
The blower in the air handler pulls hot air from your living space through the return ductwork and pushes it through the furnace then across the evaporator coil where the heat is transferred to the cold refrigerant circulating in the coil. The air is now cool and blows through the supply side of your ducting and delivered to the living space.
We are not adding cool air to your house but rather removing heat. The heat absorbed by the refrigerant in the coil travels via the lineset to the outdoor compressor where the heat is discharged by the condenser. The magic of the refrigeration process is a whole topic by itself and I have touched on it in past articles. I’ll leave that out this time to focus on the furnace/ air conditioner connection.
When the thermostat calls for cooling, a couple of things happen.
The condenser outside is given the signal to start pumping the refrigerant and the condenser fan kicks on to start moving serious air through the condenser coils.
Meanwhile, inside the fan blower on the furnace is also kicked on to get the air circulating indoors. Sometimes the control board in the furnace is bad and won’t bring on the blower or it could be that a fuse has gone out on the furnace. Either way, you won’t be cooling any air. The cooling problem is not an issue with the air conditioning components but the air handler itself.
The furnace filter also plays an import role. When the air pulled through the return is restricted by a clogged filter, not enough air is moving across the coil and it will start to ice up. This can lead to damage to the air conditioning components. So make sure you are changing your filters regularly.
If you have had a technician out to service your furnace over the winter, the cooling system is not automatically checked. They are two different systems and each need to have annual maintenance and may require repair work independently of each other.
The annual maintenance is sometimes done together, or the furnace might be checked during the winter months and the air conditioner checked in the summer months.
If they are checked together, it should be done when it is warm enough outside to properly check the refrigeration cycle. Spring is a really good time to have either (or both) of these systems checked.
Another important service issue is the draining of the condensate water that is created in the indoor coil.
High-efficiency furnaces also create condensate, which is sometimes pumped to a drain pipe. This pump is used for both the heating and cooling systems and the condensate drain tubes for both should be cleaned and checked annually or there will be water overflowing.
Sometimes dirty or clogged indoor evaporator coils can create heating problems in the winter. Just like the dirty filter scenario, the clogged coil will restrict air flow and the furnace can over heat, tripping limit switches.
So these two systems so impact each other quite a bit.
